This invention relates to photocontrols or outdoor lighting controls (OLCs) of the type which switch illuminating fixtures on and off in response to changes in ambient light, and in particular to improved outdoor lighting controls that avoid responses to short term or momentary light flashes. The invention relates to systems using such controls.
Outdoor lighting controls are generally mounted on lamp poles near the lamps they control. In one type of outdoor lighting control, the relay type, a photocell or photoresistor instantly actuates a relay. This causes the outdoor lighting control or photocontrol to respond instantly to changes in ambient light. The OLC turns a lamp on as soon as the light drops below a given level at dusk, and turns the lamp off when the light reaches a given brightness at dawn. However many outdoor lamps such as mercury vapor lamps, sodium vapor lamps, and or other high intensity discharge lamps require about five minutes to restrike once they have been shut off. Thus when an OLC shuts off mercury or sodium vapor lamps the latter remain off for about five minutes.
Accordingly, a lightning flash during the night can cause a relay type OLC to shut off a lighting system and force the lighting system to remain down during the five minute restrike time. This creates not only an inconvenience, but a security problem.
In another type of lighting control, a thermal OLC, a bimetallic strip responds slowly to current in a photocell and turns a system on and off only after a delay of about 30 seconds to 2 minutes. Such thermal outdoor lighting controls often require substantial time for installation and testing. For example, when installing an OLC a line operator performs a so-called "glove test". That is, the operator covers the photocell of the OLC to simulate darkness and then waits 30 sec-120 sec for all lamps regulated by the control to light or at least give off a glow indicating a restrike. He must then uncover the thermal OLC and wait again to make sure the lamps go off. As a final check, he may again cover the lamps to see if the lamps light or start to restrike. While such delays may appear not to be costly, a line operator is usually accompanied by expensive equipment and perhaps a ground worker. Even at only a few minutes per installation, several hours per day may be occupied waiting during the test, all at a substantial cost.